Hydraulic or electrohydraulic power steering systems for motor vehicles having a servo valve, which is arranged as a rotary slide arrangement and whose control parts—rotary slide sleeve and rotary slide—which are rotatable relative to one another are drive-coupled to one another by a torsion element which sets the control parts in a normal position relative to one another, and having a steering gear which is arranged, for the purpose of transmitting drive, between one of the control parts and steered vehicle wheels and is drive-connected directly or indirectly to a hydraulic servo cylinder which is controlled by the servo valve, are conventional.
A piston rod of the servo cylinder is connected to one or more steerable wheels of the vehicle in a conventional manner via tie rods and steering levers. A toothed rack, which meshes with a pinion of an electric servo motor or a pinion of a mechanical steering shaft connection to a steering handle, is connected in series with the piston rod of the servo cylinder (cf. German Published Patent Application No. 195 41 749 or European Published Patent Application No. 0 708 011).
The series connection of the piston rod and the toothed rack results in a large installation length of an actuator for an electrohydraulic power steering system. As a result, only relatively short tie rods are possible, which lead to unfavorable kinematics of an axle, to large steering inclination angles and sweep angles of the tie rods and to high loading, in particular in commercial motor vehicles, of an electrohydraulic power steering system and its actuator. In addition, electrohydraulic power steering systems of this type are designed, in terms of their steering power, for the respective vehicle in which they are used, and are somewhat inflexible in use.